1. Field of the Invention
One embodiment of the present invention relates to a semiconductor device and a method for manufacturing the semiconductor device.
In this specification, the semiconductor device refers to all the devices that operate by utilizing semiconductor characteristics. For example, electro-optical devices, semiconductor circuits, and electronic devices are all included in the category of the semiconductor device.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor using a semiconductor thin film formed over a substrate having an insulating surface (also referred to as a thin film transistor (TFT)). The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). A silicon film is widely known as the semiconductor thin film applicable to the transistor. As another film, an oxide semiconductor film has attracted attention.
An improvement in performance of a semiconductor device including the transistor requires an improvement in on-state characteristics and achievement of high-speed operation of a transistor including an oxide semiconductor film. As a method to improve the on-state characteristics of the transistor, the following method is known: nitrogen is injected to reduce resistance of the oxide semiconductor film and thus reduce contact resistance between the oxide semiconductor film and a source electrode layer and contact resistance between the oxide semiconductor film and a drain electrode layer.
For example, Patent Document 1 discloses a field-effect transistor in which an amorphous oxide semiconductor film containing zinc, indium, and oxygen is used, in which resistance of the oxide semiconductor film is reduced by adding nitrogen to the oxide semiconductor film by an ion implantation method, and in which a portion containing nitrogen serves as a source portion or a drain portion and a portion containing no nitrogen serves as a channel portion.